Hu Shiwen, Zheng Lirong, Zhang Hanyue, Chen Guojun, Yang Yang, Ouyang Zhuozhi, Chen Shuling, Gao Kun, Liu Chongxuan, Wang Qi, Liu Tongxu
National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China; State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of the Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, People's Republic of China.
Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
J Colloid Interface Sci. 2023 Apr 15;636:267-278. doi: 10.1016/j.jcis.2023.01.034. Epub 2023 Jan 7.
Interactions between manganese (Mn) and iron (Fe) are widespread processes in soils and sediments, however, the abiotic transformation mechanisms are not fully understood. Herein, Mn(II) oxidation on hematite were investigated at various pH under oxic condition. Mn(II) oxidation rates increased from 3 × 10 to 8 × 10 h as pH increased from 7.0 to 9.0, whereas hematite enhanced Mn(II) oxidation rates to 1 h. During oxidation process, high pH could promote the oxidation of Mn(II) into Mn minerals, resulting in the rapid consumption of the newly-formed H, and high pH facilitated Mn(II) adsorption and oxidation by altering Mn(II) reactivity and speciation. Only granule-like hausmannite was found on the hematite surface at pH 7.0, whereas hausmannite particles and feitknechtite and manganite nanowires were formed at pH from 7.5 to 9.0. Moreover, a co-shell structured nanowire composed of manganite and feitknechtite was observed owing to autocatalytic reactions. Specifically, electron transfers between Mn(II) and O occurred on the surface or through bulk phase of hematite, and direct electron transfers in the O-Mn(II) complex and indirect electron transfers in the O-Fe(II/III)-Mn(II) complex may both have contribution to the overall reactions. The findings provide a comprehensive interpretation of Fe-Mn interaction and have implications for the formation of soil Fe-Mn oxyhydroxides with unique properties in controlling element cycling.
锰（Mn）与铁（Fe）之间的相互作用是土壤和沉积物中广泛存在的过程，然而，非生物转化机制尚未完全明确。在此，研究了在有氧条件下不同pH值时赤铁矿上的Mn（II）氧化情况。当pH值从7.0增加到9.0时，Mn（II）氧化速率从3×10⁻⁶ h⁻¹增加到8×10⁻⁵ h⁻¹，而赤铁矿将Mn（II）氧化速率提高到10⁻³ h⁻¹。在氧化过程中，高pH值可促进Mn（II）氧化成Mn矿物，导致新形成的H⁺迅速消耗，并且高pH值通过改变Mn（II）的反应活性和形态促进了Mn（II）的吸附和氧化。在pH 7.0时，仅在赤铁矿表面发现颗粒状黑锰矿，而在pH值为7.5至9.0时形成了黑锰矿颗粒以及铁钾锰矿和锰矿纳米线。此外，由于自催化反应，观察到了由锰矿和铁钾锰矿组成的共壳结构纳米线。具体而言，Mn（II）与O之间的电子转移发生在赤铁矿表面或通过赤铁矿体相，O-Mn（II）络合物中的直接电子转移和O-Fe（II/III）-Mn（II）络合物中的间接电子转移可能都对整体反应有贡献。这些发现为Fe-Mn相互作用提供了全面的解释，并对具有独特性质的土壤铁锰羟基氧化物在控制元素循环中的形成具有启示意义。
